[bug 948998] Fix bigram links with no start dates

This hard codes the start date for bigram links to the dashboard to
2013-01-01 which is a hack to force the dashboard to show all of the
responses with this bigram.


I was going to work through a more serious solution but, as I explain in the comment, there doesn't seem to be a compelling reason to do a more serious solution right now. Ergo, go for the hack now and change it later if need be.

Quick r?